Climate changes in Southern Africa; downscaling future (IPCC) projections Olivier Crespo Thanks to M. Tadross Climate Systems Analysis Group University of Cape Town

Historical change Coherent regional increases in temperature attributable to human emissions Increase in temperatures ≈ 2°C since 1900 over central southern Africa

Historical change - rainfall Observed changes in rainfall: Increase in length of dry season and daily rainfall intensity over central region (Kruger, 2006) Later onset of rains over eastern lowland regions (Tadross et al., 2005) Both the above are observable over parts of southern Africa but very heterogeneous in space and time and the physical mechanisms for the changes are poorly understood

Future change - scenarios A1: A world of rapid economic growth and rapid introductions of new and more efficient technologies A2: A very heterogenous world with an emphasis on familiy values and local traditions B1: A world of dematerialization and introduction of clean technologies B2: A world with an emphasis on local solutions to economic and environmental sustainability

Future change - scenarios

Future change - temperature

Regional temperature: -Historical observed (Black line) -Historical simulated by 21 global models (Red envelope) -Projected ranges by 21 global models red: A2 orange: A1B blue:B1 Southern Africa projected temperature change at the large scale Future change

White areas are where less than two thirds of the models agree in the direction (+/-) of the change After IPCC AR4: SPM 7 Changes in rainfall from global models Summer (SH) Winter (SH) Future change

IPCC AR4 WG1: Ch 1 What are GCMs Good For?

Scales and resolution

Downscaling The challenge of bring confident large scale projections to scales of adaptation and policy Future change

An empirically derive stochastic or quantitative transfer function conditioned by the large-scale fields from the GCM or A regional climate model (RCM) nested within the GCM fields Statistical and RCM downscaling

Potential changes in rainfall: Decreases in winter rainfall over SW Cape Increases in summer rainfall over eastern regions Summer rainfall changeWinter rainfall change Future change

JanFebMarAprMayJunJulAugSepOctNovDec Downscaling to a 0.1º precipitation grid: 6 GCMs SRES A2 forcing Future – Control anomaly

10 th percentile90 th percentile Median AR4 multi-model Downscaled mean JJA precipitation response Projected regional changes in the Western Cape rainfall

Information should be presented within the context of uncertainty and projections from multiple models – choices are informed by carefully evaluated risks ! Knowledge gaps in estimating regional climate change The impact of regional changes in other drivers are not sufficiently understood e.g. land use change, aerosol emissions - what will be the impact of increases in biomass burning ? Bridging the gap in historical and far future change – the next 20 years ? Regional ocean temperatures are only crudely represented The effect of topography as a modifier of change i.e. temperature changes at higher altitudes (will come with running models at a higher spatial resolution) How do all the above interact with the greenhouse gas forced changes ? – do they act in concert (pushing the system into further change) or mitigate some of the change ?

Current analytical challenges: There is a paucity of impact analyses which integrate climate information and may help to reduce overall uncertainties for specific sectors e.g. crop and flood risk modelling, streamflow etc. Previous analyses need to be revisited in light of improved downscaled data since the AR4 – this needs to be iterated in the future as new underpinning science becomes available The timing of changes in climate and socio-economic circumstances is poorly understood yet the timing of adaptation costs and benefits is intricately linked to these changes Changes in climate and their associated impacts will be location specific and spatially detailed analyses are required e.g. differences between mountains and valleys Enabling informed decisions

Future vs. historical change: Historical change needs to be quantified as context for future change Hard to argue for future adaptation without knowing when changes are expected to happen e.g. temperature increases are experienced now but rainfall may only change in 20 years Whilst there are good reasons for adaptation in the absence of changes in climate, historical change provides the incentive for change now e.g. increasing water-use efficiency Examples of current adaptation to changes in climate allow us to learn how effective they may be at dealing with future change e.g. shifts in planting dates

You’ve decided that your present or future livelihood is sensitive to changing or varying climate. Now what? Climate independent approach: Increase resilience – adaptation is non-climate specific Climate dependent approach: adaptation is shaped by actual or projected changes in climate or climate variability Now we need climate information Global Climate Models are at the core of all future climate projections